We had earlier suggested a mechanism for the origin of frameshift mutation. We now propose tests for our model, and will attempt to relate the frequency of mutation to the base sequence at the site of the mutation. Mutations in the bacteriophage T4 lysozyme will be examined; the frequency of mutation will be determined by selective methods that have been developed, while the base sequence will be examined by the analysis of amino acid replacements in double mutant pseudowild strains. In our model, additions or deletions of bases occur through the mis-alignment of short stretches of bases at sites in the DNA which contain repeating bases or base doublets, and which are bounded on one side by a single stranded gap. In one set of proposed experiments the frequencies of the deletion and addition of a base pair will be measured at a particular site at which the number of identical sequential base pairs is varied from four to six; in another set of experiments the base sequences of mutated sites with unusually high reversion frequencies will be determined.